AS - Gas Exchange System

James Alberts Biology ­ Gas ExchangeDiffusion is required to supply oxygen to all organisms; the efficiency of diffusion is increased if there is; 1. A large surface area ­ In which exchange of molecules can take place 2. A concentration gradient ­ In which the principle of diffusion works 3. A thin surface - Easy to pass through 4. Warmer temperature ­ More energy therefore move fasterFick's law is used to measure the rate of diffusion;(The symbol means `proportional to')So in ideal situations the larger the area and difference in concentration and the thinner the surface thequicker the rate of diffusion of molecules through cell membranes, or the phosolipid layer.In the mammals (humans) the gas exchange surface is called the alveolusThere are numerous alveoli which are basically sacs of air which are supplied by a system of tubes from thetrachea splitting into two bronchi, which mammals have two one for each lung, within these there arenumerous amounts of bronchioles which are in a general sense all connected to the outside by the mouthand nose.The alveoli provide a huge surface area in which gases can diffuse, along with this the thickness of thesurface they diffuse through is very thin, in fact only one cell thick between the lung lining and the bloodcapillary.The blood supply flowing to the lungs is very extensive meaning that oxygen is near-less instantly carriedaway and diffused into the blood.Ventilation is the name given to the movements between the concentration gradients because air is regularlymoving between the atmosphere and lungs.This breathing in or named as inspiration and breathing out named as expiration is controlled by nervousimpulses from the respiratory centre in the medulla of the brain, located at the centre back. From this boththe intercostals muscles which are located in between the ribs and the diaphragm receive impulses from therespiratory centre. Stretch receptors in the lungs send impulses to the respiratory centre in the brain givinginformation about the state of the lungsThe process of breathing in or as I mentioned is called inspiration, the process is shown below; 1. External intercostals muscles contract 2. Ribs move up and out 3. Thorax width increases in both measurement ways 4. Diaphragm contracts and moves down to flattenFrom these stages the volume that the thorax has increased which means pressure between the pleuralsurfaces decreases, air pressure in alveoli is less than atmospheric pressure, which air is then forced into thelungs due to the lower pressure within them.As the lungs fill with air the stretch receptors send impulses to the expiratory part of the respiration centre toend breathing in.The process of breathing out is called expiration, the process is shown below;

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External intercostals muscles relax 2. Ribs move down and inwards 3. Thorax decreases in both measurement ways 4. Diaphragm relaxes and moves upFrom these stages the volume of the thorax has decreased, which means pressure between the pleuralsurfaces increases, air pressure is more than atmospheric pressure, which air is then forced back out of thelungs, due to the higher pressure within them.…read more